Teachers' leaders had mixed feelings on hearing that huge sections of an education bill were dropped today in the rush to pass legislation ahead of the dissolution of parliament.

Christine Blower, general secretary of the National Union of Teachers, was "delighted" a clause that would have forced teachers to hold a licence that needed renewing every five years had been dropped. The aim had been to weed out bad teachers.

She was equally pleased that New York-style report cards to rate primary and secondary schools had been ditched. Blower said the report cards would have "reduced schools to a single letter or number, which was not the right way to do it".

But she said it was a shame that a reform had fallen which promised one-to-one lessons for primary school pupils who fail to reach the expected levels in literacy and numeracy. These lessons would have helped to guarantee funding in schools for pupils who needed extra help, she said.

Chris Keates, general secretary of the Nasuwt union, said the Conservatives stopped this clause becoming law because they want one-to-one tuition to "remain the preserve of those with money, who seek to buy advantage for their children".

An overhaul of the primary curriculum, which would have marked the biggest change to primary schooling in a decade, has been removed. It emphasised traditional areas of learning – including phonics, the chronology of history, and mental arithmetic. Keates said it would have given teachers more flexibility and autonomy over what they taught.

"Why would the Tories want to reject these things, if not to create a free-for-all in which only the strongest, the wealthiest and the most privileged survive?"

Other groups, such as the British Humanist Association (BHA), said the removal of a reform to make sex education mandatory in all schools was "catastrophic".

Schools would have had to teach about contraception and the importance of stable relationships, including marriage and civil partnerships. Faith schools would have been free, as now, to express the views of their faith, but would not have been allowed to suggest that their views are the only ones.

Andrew Copson, chief executive of the BHA, said: "For the first time in the history of the national curriculum, the new primary curriculum would have included the study of evolution – a move that had huge support from scientists and teachers. It is deeply concerning that this most fundamental of biological concepts will now remain off the primary curriculum."

Mandatory sex education in schools would have helped reduce unwanted pregnancies and infections, he said. It would also have corrected misleading notions about sex that teenagers sometimes pick up.

"There was massive support for its implementation from health professionals, teachers, parents and young people themselves. The loss of these subjects as core parts of the curriculum is catastrophic," he said.

Charities went further and said it was a "disgraceful betrayal of the next generation".

Lisa Power, policy director of the Terrence Higgins Trust, said: "The government does not have an excuse that they did not know the date that the election was coming.

"We will see the impact on young people who haven't had decent sex and relationships education: the girl who gets pregnant because the only education she got was in the playground, the people who use the word 'gay' as an insult. It's a disgraceful betrayal of the next generation. There's been very widespread agreement that young people need better sex and relationships education."

Julie Bentley, chief executive of the Family Planning Association, said: "We were on the verge of witnessing a historic breakthrough in the sexual health education of children and young people in England.

The schools secretary, Ed Balls, was locked in disagreement with his Conservative counterpart, Michael Gove. The Tories said they were against the government's refusal to allow parents to withdraw children who were under the age of consent from attending sex education classes they considered inappropriate.

A Conservative spokesman said: "The government torpedoed its own proposals. We wanted progress on sex education, but the government preferred petulance. We agreed an all-party way forward to guarantee high quality sex education which respected the rights of parents and faith groups."

Balls said: "There is now widespread agreement that statutory PSHE (personal, social, health, and economic education) is essential to prepare young people for adult life, and our reforms would ensure that by reducing the age of parental opt-out to 15, all children receive at least one year of compulsory sex and relationship education.

"This is a very significant setback, which will deny many young people proper and balanced sex and relationship education."